In this application, the distributor according to the invention will be described as a component of a system for spreading fertilizer. However, within the scope of the invention, the distributor can easily be adapted to many other applications. Two examples of such applications are salt spreaders and water spreaders.
A system for spreading fertilizer is usually mounted to a tractor and comprises a central tank containing the fertilizer, means to pump the fertilizer out of the tank, and a number of nozzles through which the fertilizer is output to the target environment.
It is typically desired to control how much fertilizer is output by each nozzle. However, the control of this quantity depends upon a large number of variables. For example the flow rate of the fertilizer out of each nozzle will be dependent on the type of fluid, the temperature of the fluid, the pressure in the system, the geometry of the nozzle, etc. In addition it is typically desired to control the amount of fertilizer output by the system as a function of the speed of the tractor. The faster the tractor drives, the higher the fluid flow should be in order to keep the amount of fertilizer being spread on the ground the same.
The amount of flow out of each nozzle is typically controlled by a combination of varying the pressure of the fluid and by changing the size of an orifice located in each nozzle.
In some of the prior art, such as U.S. Pat. No. 3,815,830 the entire nozzle is changed to change the flow rate. In other, more recent, prior art, nozzles have been designed with “orifice plates”. An orifice plate is a plate with a fixed sized hole in it. Different orifice plates are available with different sized holes. By putting different orifice plates in a nozzle, the flow output for the nozzle can be changed.
Up to 100 orifice plates with orifices of differing sizes are available for a typical nozzle. Said orifices typically range in size from 0.1 to 3 mm in diameter. In addition, a large spraying machine can have up to 100 nozzles. This results in a large number orifice plates which need to be kept in stock.
The orifice plates are usually changed manually. The nozzle is opened up, the orifice plate taken out, a new orifice plate set in, and the nozzle closed up again. This is very time consuming, especially for the larger sprayers with a large number of nozzles. In addition there is a risk of getting contaminants inside the nozzle, which could block the nozzle and prevent it from functioning properly.
GB patent 1,068,895 presents a liquid fertilizer distributing apparatus designed to overcome the above-mentioned problems. The apparatus comprises a manifold, which distributes fertilizer to two independent nozzles. The manifold comprises a circular disc with two identical series of orifices of varying size placed around the circumference of the disc. The fluid from the tank is directed into two paths, each flowing through an orifice in the circular disc. After passing through the orifices, the two fluid paths are directed to nozzles. When the flow rate is to be changed, the circular disc is rotated thereby changing the orifice size. This invention therefore solves the problem of having to manually change all the orifice plates. However, the solution is limited to systems having a small number of nozzles. Additional nozzles require additional orifice series, spaced circumferentially. This requires quite a large amount of space. For example, consider the disc required for a system with 100 nozzles. This would require 100 circumferentially spaced series. Another issue with this solution is that there are a number of different sized orifices on the same plate which also makes the metering disc larger.